Harnessing rhizosphere Bacillus and Epichloë symbionts to promote the performance of Achnatherum inebrians within arid ecosystems

Abstract

Plants in natural ecosystems form intimate associations with diverse microorganisms, including bacteria and fungi, collectively termed the plant-associated microbiota. Notably, the entire rhizosphere microbial community is widely recognized as the plant's second genome, crucial for host growth and health. Achnatherum inebrians, a perennial grass increasingly dominant in the arid/semiarid grasslands of northwest China, is almost universally colonized by Epichloë fungal endophytes. We isolated bacteria from the rhizosphere soil of Epichloë endophyte-infected (E+) and endophyte-free (E-) plants of A. inebrians. A total of 393 bacterial isolates were identified, primarily belonging to Proteobacteria (195), Actinobacteria (100), and Firmicutes (98) at the phylum level, with dominant genera including Acinetobacter (45 isolates), Pseudomonas (90 isolates), Rhizobium (60 isolates), Bacillus (98 isolates), and Arthrobacter (100 isolates). E+ plants exhibited significantly higher relative abundances of Bacillus and Pseudomonas compared to E- plants. E+ plants showed significantly enhanced germination potential, germination index, seedling length, and fresh weight (P<0.05) compared to E- plants. Inoculation of selected Bacillus isolates onto A. inebrians seedlings demonstrated their growth-promoting ability. All isolates of Bacillus improved germination rate, germination potential, germination index, root length, seedling length, fresh weight, and dry weight (P<0.05). Based on membership function analysis, 80 out of 90 Bacillus isolates positively influenced seed germination of A. inebrians. Both Epichloë endophytes and Bacillus significantly increased tiller number, fresh weight, and dry weight (P<0.05), while their interaction notably affected plant height and reproductive branch number (P<0.05). These findings highlight the synergistic role of Epichloë spp. and rhizosphere bacteria in enhancing host plant performance. Future research will focus on constructing synthetic microbial communities to leverage these beneficial plant-microbial interactions for sustainable agricultural practices.